So how much would this cost in taxes? Quite a bit. At the moment, Social Security is expected to experience a funding shortfall by 2033. Congress will need to raise taxes by between 1 and 1.5 percent of GDP just to maintain current benefits. On top of that, the expanded benefits proposed by New America would cost an estimated 3.7 percent of GDP. The net cost: About 5 percent of GDP.

This plan is so outlandish that even the Wonkblog author admits it's going nowhere fast:

Needless to say, this isn’t the sort of proposal Congress is likely to take up anytime soon. Hiking taxes by 5 percent of GDP is far outside the bounds of what either party is contemplating.

No kidding, especially so since payroll taxes are paid by all workers and the burden can't be shifted to the "rich." But I also object to the idea that this creaky, Depression-era program that already has a negative rate of return should be expanded because some Americans mistakenly believed it would be a sole source of retirement support. These silly counter-intuitive studies are good for a headline and nothing else.